1. Field of the Invention
The present invention relates to a positive active material for primary electric cells which are to discharge at a constant voltage level, and more particularly to a positive active material composed principally of silver oxides.
2. Description of the Prior Art
It is known that when silver peroxide discharges, it passes through the monovalent silver oxide state, resulting in the disadvantage that discharge occurs at two voltage levels of unequal duration. This disadvantage can be avoided by use of monovalent silver oxide, which discharges at a single voltage level, but this results in an appreciable reduction of storage capacity for the same cell dimensions.
It has been proposed recently to use silver peroxide as the main active material, but to dispose a layer of monovalent silver oxide between the cathode current collector and the silver peroxide. The monovalent silver oxide is impermeable to the electrolyte and is the first of the oxides to discharge. The discharge of the monovalent silver oxide produces metallic silver, which reacts with the silver peroxide to form additional monovalent silver oxide, which discharges in its turn, and so on. In this way, the silver peroxide effectively discharges at a single voltage level, that of the monovalent silver oxide.
The resulting structure of the cell is complicated, however, because the active material must be disposed in several successive layers. Furthermore, silver peroxide is not very stable; it tends to decompose, evolving oxygen. The result is that when cells in which the active material constitutes silver peroxide, even in part, internal overpressures occur which can lead to the bursting of the cell.